It's free

Pixel Dungeon is absolutely free, no ads, no pay-to-unlock features.
I'm making this game for fun and I'm not going to monetize it.
Nevertheless people ask sometimes, is there a way to support
the developer (that is me), so I've added the "Donate"
button (via PayPal) at the top of this page
for anyone interested ☺.

Update 1: Since the version 1.6.0 it is possible to make a donation
right from the game (there is a semi-transparent button on the main screen)
as an in-app purchase.